FOREST HEALTH

CommonCommon InsectsInsects andand DiseasesDiseases ofof InteriorInterior Douglas-firDouglas-fir

rees play an important aesthetic and Tbiological role in our environment. Trees such as Douglas-fir can suffer

from a wide variety of native and

introduced pests. This guide is intend-

ed to help non-specialists recognize

common ailments of Interior Douglas-

fir and diagnose the likely cause.

Using this guide, you may be able to

determine an appropriate treatment

for your tree or better describe the

problem to a tree care professional. WhereÕs the Problem?

Foliage or branches Insects that feed on needles are affected: called defoliators. Caterpillars, the Foliage discoloured or pre-adult form of absent. Frass or web- butterflies and bing present...see moths, are com- defoliating insects mon defoliators. Branches swollen How to with prolific produc- Dwarf mistletoes tion of shoots and produce conspicu- Recognize foliage...see dwarf ous swellings of mistletoes branches and Interior Douglas-fir growth of aerial Foliage discoloured or shoots. Interior Douglas-fir (Pseudotsuga mottled. Small menziesii) is one of British bumps or blisters on Symptoms of Columbia’s largest tree species, leaf surface...see foliar problems foliar problems growing to 42 m in height. are chlorosis or Foliage covered discoloration, Its needles are of equal length with small, cottony bleaching, shrivel- (approximately 2.5 cm long), tufts...see foliar ling, twisting, or and are flat, soft, narrow, problems/adelgids dropping of and only slightly sharp. These needles. needles stand out from three Whole tree sides of a twig. The buds are affected sharply pointed. Seed cones (declining): Bark beetles are some of the are 5–11 cm long and are easily most damaging Mature tree identified by the three-pronged forest insect pests. bracts that emerge below each Crown discoloured They attack trees bright yellow, red, scale. Young trees have smooth by boring into the or brown inner bark and grey-brown bark covered with ...see bark beetles laying eggs. resin-filled blisters. Mature Tree any age trees have thick, reddish Root diseases are Gradual thinning of brown bark that is deeply caused by a group crown and yellowing of fungi. Over sev- ridged with furrows. foliage...see root eral years, infected diseases trees will weaken as the root system deteriorates.

Main stem: Wood decay fungi Conks (bracket survive on the Bark of a young Douglas-fir fungi) visible on woody tissue of stem...see wood trees and cause decay fungi decay in the heartwood and sapwood.

Insects and disease Abiotic problems can afflict all are caused by the portions of the elements and interior Douglas- may damage or Bark of a mature fir: needles, bark, kill trees. Douglas-fir wood, and roots.

2 Defoliating insects Dwarf mistletoe

efoliators are insects warf mistletoes are plants that feed on the nee- that parasitize a living host actual size Ddles or leaves of trees. Spruce budworm Dtree, robbing it of nutrients Caterpillars, the pre-adult or larval and water. This pest infects trees of form of butterflies and moths, are Spruce budworm is a serious pest of any age but is quite host-specific, common foliage-eating pests of Douglas-fir forests in the interior of preferring only a few species. conifers, including Douglas-fir. British Columbia. The full-grown lar- Douglas-fir dwarf mistletoe primari- Symptoms of damage include discol- vae have hairless, reddish to olive- ly affects Interior Douglas-fir. oration or loss of foliage (in general, brown bodies and each body segment from the top of the tree downward has four distinct light-coloured spots. Dwarf mistletoe spreads via seeds and from branch tips inward); Young larvae mine needles and buds, that are ejected from their pods in chewed needles on the tree or and feed on new foliage. Mature lar- the fall. These ground; silken webbing; frass (insect vae may feed on older foliage. seeds land on droppings) accumulations under the adjacent tree; and abundant caterpillars, The rusty tussock moth caterpillar Douglas-fir pupae, pupal cases, or adult moths. looks very similar to the Douglas-fir foliage and ger- tussock moth caterpillar; however, minate, pene- actual size trating through the bark. After 2–3 years, the branch swells around the point of infec- tion, and aerial Aerial shoots shoots containing flowers are produced.

While mainly an aesthetic problem, if enough dwarf mistletoe brooms Douglas-fir tussock moth larva occur on a tree they will drain suffi- cient nutrients to reduce tree vigour and growth, leaving the tree suscep- The Douglas-fir tussock moth is a the nodes from which the tufts arise tible to attack destructive native defoliator of are orange instead of red. The four by other pests. Douglas-fir trees throughout the brushes on its back are golden. This Large over- semi-arid portions of British caterpillar also feeds on many other head brooms Columbia. The sides and posterior tree species including deciduous trees. may also portions of the caterpillar's body are break off in covered with hairy tufts that arise Defoliator populations usually cycle high winds, from small red nodes. Four thick, between outbreak levels and unde- posing a safe- brown and cream-coloured tufts or tectable numbers. The combined ty hazard. brushes are found on its back. Two effects of predators, parasites, disease, long, black tufts arise from either side weather, and food availability of the head and one from the rear. naturally control populations.

Douglas-fir mistletoe brooms 3 Foliar problems

oliar diseases are most notice- able the year after infection Foccurs, particularly if the pre- vious spring was wet with mild tem- peratures. A foliar disease, such as Cooley spruce gall adelgid “wool” on kinked needles Upper side of needles (L) and the Douglas-fir needle blight, produces aphid-like Adelges cooleyi on the small, dark spots on one-year-old mottled and twisted, and may drop underside of needles (R) needles. These are clearly visible in prematurely. Light infestations are the spring, just before the affected common, yet not seriously damaging. The earliest evidence of attack by needles drop. Most foliar diseases do Damage is usually less conspicuous Douglas-fir beetle is reddish boring not warrant treatment, as they will on older trees. Small trees stressed by dust on the bark below beetle persist only for a year or two. Trees environmental conditions are often entrance holes. This may occur from will suffer only if they lose foliage more heavily infested. the base of the tree to the midpoint over several consecutive years or if on the main stem and is most distin- new foliage is repeatedly infected. guishable in the spring. Bark removal In these cases, you may consider around these holes will reveal applying a fungicide to reduce the gallery systems. frequency or severity of infection. Douglas-fir beetle

Bark beetles

ark beetles generally attack large, mature trees. BThe Douglas-fir beetle prefers felled trees, slash, stumps, and windfall as well as trees that have been damaged or stressed by factors such as the urban environ- ment, defoliators, or root disease. Typical symptoms of foliar disease actual size Adult Douglas-fir beetles are small, The Cooley spruce gall adelgid, an 4–7 mm, cylindrical, and usually aphid-like insect, alternates between brown or black. They bore into the two hosts, Douglas-fir and spruce. bark of trees and lay eggs in galleries It is named for the cone-like galls or tunnelled under the bark. Larvae swellings it causes on the branches of hatching from the eggs feed on the spruce trees. This insect is extremely inner bark. Adults may also introduce small — the adults are approximately a fungus, which, along with larval 0.1 cm long. Adults, which are com- feeding, usually kills the tree. pletely covered with a white, waxy “wool”, appear as white tufts on the The foliage of an attacked tree underside of needles, on new shoots, usually changes from green to pale and on developing cones. yellow-green to red by the spring of the year following the initial attack, Attacked needles may be yellow or before dropping. Bark beetle larval galleries

4 Root diseases

oot diseases are a group of fungi that attack healthy tree Rroots, interrupting the flow of water or nutrients to the crown, caus- Laminating of rotting wood caused by Phellinus weirii ing a decline in tree vigour. Usually, young trees die more quickly than Pitting of wood caused by laminated root rot older ones. Living infected trees may Prolonged decay by laminated root blow over because their root systems rot, caused by Phellinus weirii, creates are structurally weakened. Root dis- small pits in the wood. Eventually eases spread primarily by contact this decaying wood separates into between infected roots and neigh- sheets along the annual growth rings. bouring uninfected roots. Depending Red-brown mats of hair-like fungal on the root disease, the roots of dead mycelia may be found between trees and stumps may remain infec- sheets of decayed wood. This fungus tious for many years. rarely produces fruiting bodies.

Infected trees may show one or more of these symptoms: yellow- ing or thinning foliage; gradual shortening of leader growth (“rounding” of the crown); or a heavy crop of small cones. Infected trees that are wind- thrown usually have small root balls with few remaining fine roots. Additional signs and symptoms are specific to the root disease. Note the dark streaks in the sapwood caused Armillaria fruiting bodies can appear in the by blackstain Armillaria root disease, caused fall at the base of an infected tree by Armillaria ostoyae, may pro- duce minor to copious resin Blackstain root disease, caused by flow (pitching) at the base of Leptographium wageneri, is a vascular an infected tree. Whitish, wilt. This means it causes little fan-like fungal mycelia will degradation of the roots, but instead be found between the bark kills by interrupting the flow of water and wood. Honey-coloured within the tree. The fungus produces mushrooms may appear at a brown to black stain, which can be the base of infected trees in identified by cutting into the last few the fall. Extended decay pro- years of wood growth. This fungus is duces a stringy type of white transferred to host trees mainly by rot. This disease is common root beetles, less often directly from in the interior. root to root. It does not produce a Armillaria mycelia under the bark of a root or at the visible fruiting body. base of a tree

5 Decays are generally split into two groups: brown rots and white rots. Brown rots darkly stain the wood, which eventually degrades into a brittle, cube-like structure. White rots cause lighter staining and the wood becomes pitted or mottled, Wood decay fungi eventually degrading into a stringy Abiotic problems structure or separating along annual group of fungi called bracket rings into sheets. ouglas-fir, depending on (or conk) fungi cause decay seasonal weather patterns, Aof tree wood. These fungi Decay fungi normally progress Dcan suffer from sunscald, survive by breaking down the compo- slowly. The presence of conks usually drought, or frost. Drought is difficult nents of wood tissue and absorbing indicates that wood decay is well to recognize because the effects may the resulting nutrients. Decay fungi advanced—the tree is probably not appear until the following year — may enter trees through wounds, structurally unsound and subject far too late for corrective action. broken or dead branches, or roots. to breakage. Drought-stressed trees will usually If a conk is not present, a suspect tree drop all or a portion of their foliage may be drilled to see if the stem wood the spring following a dry summer, is still sound. These drill holes can be often with little colour change. capped with putty or silicone to pre- Mortality of the top of the tree or vent insects or fungal spores from the whole tree can occur. This will entering. be more common in areas where Douglas-fir is a marginal species. An example of a common wood Juvenile trees and those growing decay fungus is Fomitopsis pinicola. on rocky or porous soils will suffer It produces a brown crumbly rot that the most. is not usually evident until the tree falls. The only external indicator is Tree foliage and bark protected from Fomitopsis pinicola fruiting the direct rays of the sun may body and decay the fruiting body. become damaged by sunscald if Insects such as wood borers, carpenter exposed abruptly. Foliage may ants, and dampwood termites are become scorched and drop prema- often associated with decaying wood. turely but will usually recover. Bark, usually on the southwest side of the main stem, may be damaged after thin- ning or pruning if the heat of direct sun damages or kills the cambium under- neath. Damaged areas will usually appear copper to bright red, marking the extent of the damage. This colour

Brown rot – This cube-like type fades gradually and of wood decay is typical of will be distinguished most brown rot by the flattened

White rot – This pitted type of Sunscald lesion appearance of the decay is common to many stem as the tree white rots 6 grows around the wound. In some cases the bark may fall off altogether. How Can I Control These Pests? Most times the tree will recover. These general guidelines will show you how to control pest infesta- Frost damage typically occurs in the tions. Consult a specialist before using any insecticide. spring when low temperatures freeze the sensitive tissues of newly flushed Douglas-fir trees, though fairly tolerant to defoliating buds. Late-season frosts more uniform- insects, may be killed if attacked year after year. In ly affect the entire tree, causing needles these cases, apply an approved insecticide, especially to and small twigs to die. Unless frost preserve special or high-value trees. damage is severe, older trees should Dwarf mistletoe brooms and branch infections should survive but may become deformed if be pruned. This will reduce stress on the tree and the leader is killed repeatedly. Frost reduce future infections. may kill young trees outright. Damage caused by adelgids will rarely need to be treated because it is usually not significant except on seedlings or small saplings. Insecticides registered and recommended for aphids are usually effective if applied when the adelgid is first noticed.

Trees attacked by Douglas-fir beetles rarely survive. Cut down infested trees as soon as possible and burn the bark to kill any living beetles and to prevent the spread of these insects to nearby susceptible trees.

Carpenter ants may be a nuisance as well as cause serious structural damage to wood construction. Because dead and down trees, waste wood, and firewood are likely to harbour Frost damage ant colonies, clear these materials away from buildings.

When bracket fungi, or conks, appear on the tree, it usually indicates well-advanced decay. The wood will have deteriorated to the point where the tree may be structurally unsound, allowing the stem to break. Remove such trees, as they can pose a safety hazard.

Few options are available to treat trees afflicted with root disease. Remove any infected dead or obviously weakened trees from the area, as they will pose a hazard to humans and property. Ideally, also remove infected stumps because they can harbour the fungi for many years and will spread the disease to newly planted Douglas-fir or other susceptible neighbours. If stump removal is not possible, use the following table to restrict your choice of future plantings near infected stumps.

If tree dies from: Do not replace with:

Armillaria ostoyae Douglas-fir, true firs, spruce, cedar, hemlock, pine Phellinus weirii Douglas-fir, true firs, hemlock Leptographium No restriction

7 For further information, please contact:

Ministry of Forests Forest Health

Nelson Forest Region, 518 Lake Street, Nelson, B.C. V1L 4C6 (250) 354-6200

Kamloops Forest Region, 515 Columbia Street, Kamloops, B.C. V2C 2T7 (250) 828-4131

Cariboo Forest Region 200-640 Borland Street Williams Lake, B.C. V2G 4T1 (250) 398-4345

Or via Enquiry BC: • In Vancouver – 660-2421 • In Victoria – 387-6121 • Elsewhere in B.C. – 1-800-663-7867

Internet contact:

Ministry of Forests – www.for.gov.bc.ca Canadian Forest Service – www.pfc.cfs.nrcan.gc.ca Insect Diagnostics – www.forestry.ubc.ca/fetch21/FRST308/labindex.html Brochure URL Address – www.for.gov.bc.ca/hfd/pubs/docs/sil/sil471.htm

Ministry of Forests

printed on recycled paper 8 ISBN 0-7726-7703-4 SIL-471